Hello UNGJIN P! I'm Gunasekar and I'd be happy to help you with your question.
I understand that you keep getting the OneDrive storage full message on your despite your storage seems free.
Do you have multiple Microsoft accounts?
a. Open any web browser and select incognito mode.
b. Go to https://onedrive.live.com/
c. Sign in with your Microsoft account.
d. Check the storage occupied.
If the storage is below the limit and if you are still receiving messages, e-mail the OneDrive support team.
https://onedrive.live.com/?action=feedback
If you are getting one-time codes repeatedly, it is recommended to check your account recent activity page to see if someone trying to access your account.
a. Go to https://account.live.com/Activity and sign in with your Microsoft account.
b. Select recent activity.
c. If you see account activity that you're sure wasn't yours, let us know and we'll help you protect your account. If it's in the Unusual Activity section, you can expand the activity and select It wasn't me. If it's in the Recent Activity section, you can expand the activity and select Protect your account.
However, it is recommended to keep your Microsoft account safe and secure by following the suggestions below.
- Create a strong password.
- Enable two-factor authentication.
- Delete unused devices from your account.
Here's the related article for your reference:
https://support.microsoft.com/help/628538c2-7006-33bb-5ef4-c917657362b9
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I hope this information helps. If you have any questions, please let me know and I will be happy to help you further.
Best regards,
Gunasekar N